<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <div id="d1" class="c1">div~~666</div>
</head>
<body>
        <script>
            let c1=document.getElementsByTagName("div")
            // let  d1=document.getElementById("d1")
            alert(d1.innerHTML)
        </script>
</body>
</html>